Indoxyl sulfuric acid is a tryptophan metabolite derived from food protein and is known as a uremia substance. The uremia substance is stored in the body with progress of renal dysfunction and causes uremia symptoms, such as loss of appetite, nausea, and vomiting. In actual, it has been reported that the concentration of indoxyl sulfuric acid in serum markedly increases in chronic renal failure patients and is about 60 times that of normal persons (e.g., Non patent literature 1). Therefore, it is very useful for diagnosis and examination of diseases to measure the indoxyl sulfuric acid concentration in serum. Further, the measurement method can be utilized for the judgment of therapeutic effects, prognostic prediction, selection of prescription foods of dietary therapy, and the like.
Heretofore, the measurement of indoxyl sulfuric acid has been performed mainly using gas chromatography and high performance liquid chromatography. These methods have been excellent in sensitivity or accuracy but have had problems in that skill has been required for analysis, high cost has been required for measuring devices or facilities, and the like. On the other hand, an EIA method (enzyme immunoassay) using an antibody specific to indoxyl sulfuric acid has been reported as a method for measuring indoxyl sulfuric acid without using the devices (e.g., Patent Literature 1). However, the measurement method utilizing an antigen-antibody reaction has had problems in that the measuring time is long and an operation for the measurement is complicated.
Under the circumstances, a development of a method capable of simply measuring indoxyl sulfuric acid concentration rapidly and correctly without using an expensive measuring device has been demanded.